Multicast communication method and system

Abstract

In delivery of data from a sender terminal to a plurality of receiver terminals via a network, a data packet a certain receiver terminal has lost is recovered by retransmission from a neighboring receiver terminal. Each receiver terminal has a negative acknowledgement (NACK) timer and a retransmit packet timer. A retransmission control section determines a set value for these timers according to the number of times of retransmission, the network propagation delay time, the number of receiver terminals and the permissible delay time so that the delay time from detection of loss of a data packet until arrival of a retransmit packet falls within the permissible delay time that was determined with the capacity of a receiver buffer.

What is claimed is:  
     
         1 . A multicast communication method for multicasting data from a sender terminal to a plurality of receiver terminals via a network, the method comprising steps of: 
 enabling a receiver terminal among the plurality of receiver terminals, having detected loss of a data packet to be received, to multicast a negative acknowledgement after a lapse of a predetermined time controlled by a first timer; and    enabling another receiver terminal among the plurality of receiver terminals, having received the data packet normally and also received the negative acknowledgement, to multicast a retransmit packet after a lapse of a predetermined time controlled by a second timer,    wherein the method further comprises a step of determining a timer set value for the first timer or the second timer so that the delay time from the detection of loss of the data packet until arrival of the retransmit packet falls within a permissible delay time.    
     
     
         2 . The method of  claim 1 , wherein the step of determining a timer set value comprises a step of determining the set value according to a propagation delay time between the sender terminal and the plurality of receiver terminals and the number of receiver terminals.  
     
     
         3 . The method of  claim 1 , wherein the step of determining a timer set value comprises a step of determining the set value according to the number of times of retransmission designated.  
     
     
         4 . A multicast communication system for multicasting data from a sender terminal to a plurality of receiver terminals via a network, comprising: 
 means for enabling a receiver terminal among the plurality of receiver terminals, having detected loss of a data packet to be received, to multicast a negative acknowledgement after a lapse of a predetermined time controlled by a first timer; and    means for enabling another receiver terminal among the plurality of receiver terminals, having received the data packet normally and also received the negative acknowledgement, to multicast a retransmit packet after a lapse of a predetermined time controlled by a second timer,    wherein the system further comprises means for determining a timer set value for the first timer or the second timer so that the delay time from the detection of loss of the data packet until arrival of the retransmit packet falls within a permissible delay time.    
     
     
         5 . The system of  claim 4 , wherein the means for determining a timer set value comprises means for determining the set value according to a propagation delay time between the sender terminal and the plurality of receiver terminals and the number of receiver terminals.  
     
     
         6 . The system of  claim 4 , wherein the means for determining a timer set value comprises means for determining the set value according to the number of times of retransmission designated.